Re: Why does the enhancer create a PROTECTE no-args constructor by default?

[Rick Curtis <cu...@gmail.com>]

David-

Per the JPA spec --

The entity class must have a no-arg constructor. The entity class may have
other constructors as well.
The no-arg constructor must be public or protected.

...so if your Entity doesn't have one, OpenJPA will do it for you.
-- 
Thanks,
Rick

On Fri, Dec 4, 2009 at 1:29 PM, KARR, DAVID (ATTCINW) <dk...@att.com>wrote:

> I'm reading the OpenJPA doc, and I see that the enhancer creates a
> protected no-args constructor if there is no public one.  Why exactly
> does it do that?  What is the point of creating a protected constructor
> instead of letting the JVM create the public one?  The doc only says
> that it does this, not why.
>

RE: Why does the enhancer create a PROTECTE no-args constructor by default?

["KARR, DAVID (ATTCINW)" <dk...@att.com>]

> -----Original Message-----
> From: Michael Dick [mailto:michael.d.dick@gmail.com]
> Sent: Friday, December 04, 2009 1:54 PM
> To: users@openjpa.apache.org
> Subject: Re: Why does the enhancer create a PROTECTE no-args
> constructor by default?
> 
> Hi David,
> 
> The JVM will create a no-arg constructor if you have no other
> constructors.
> The spec requires a no-arg constructor so that the persistence
provider
> can
> create an empty instance. OpenJPA uses it via some tricky generated
> code
> (bytecode insertion).
> 
> As for why it's protected instead of public I presume the original
devs
> thought it was safer to restrict access to the generated constructor.
> It
> isn't documented in the manual, but you could go diving in
> PCEnhancer.java
> (which generates the constructor) and see if there are any comments
> that
> shed some light on the rationale.

Nope, not a word.  The "enhanceClass()" generates the constructor as
public if it's externalizable, private if it's final (which is odd, as I
thought you couldn't have final persistent classes), and protected
otherwise.  No indication why.  There was a comment about making it
public if the class was externalizable, but nothing else.

> On Fri, Dec 4, 2009 at 2:55 PM, KARR, DAVID (ATTCINW)
> <dk...@att.com>wrote:
> 
> > > -----Original Message-----
> > > From: Rick Curtis [mailto:curtisr7@gmail.com]
> > > Sent: Friday, December 04, 2009 12:31 PM
> > > To: users@openjpa.apache.org
> > > Subject: Re: Why does the enhancer create a PROTECTE no-args
> > > constructor by default?
> > >
> > > David-
> > >
> > > Per the JPA spec --
> > >
> > > The entity class must have a no-arg constructor. The entity class
> may
> > > have
> > > other constructors as well.
> > > The no-arg constructor must be public or protected.
> > >
> > > ...so if your Entity doesn't have one, OpenJPA will do it for you.
> >
> > Ok, I'll phrase the question again, and perhaps I can make it more
> > obvious this time.
> >
> > Why does the enhancer create a PROTECTED no-args constructor, and
not
> a
> > PUBLIC one?
> >
> > If it was going to create a PUBLIC constructor, there'd be
absolutely
> no
> > point to this, because that's exactly what the JVM does.  If the
> > enhancer had a good reason to create a PROTECTED constructor instead
> of
> > a PUBLIC one, then I can see why the enhancer would do this, but I
> still
> > see no obvious reason to create a PROTECTED constructor.
> >
> > Is that clearer now?
> >
> 
> > > --
> > > Thanks,
> > > Rick
> > >
> > > On Fri, Dec 4, 2009 at 1:29 PM, KARR, DAVID (ATTCINW)
> > > <dk...@att.com>wrote:
> > >
> > > > I'm reading the OpenJPA doc, and I see that the enhancer creates
> a
> > > > protected no-args constructor if there is no public one.  Why
> > exactly
> > > > does it do that?  What is the point of creating a protected
> > > constructor
> > > > instead of letting the JVM create the public one?  The doc only
> says
> > > > that it does this, not why.
> > > >
> >

Re: Why does the enhancer create a PROTECTE no-args constructor by default?

[Michael Dick <mi...@gmail.com>]

Hi David,

The JVM will create a no-arg constructor if you have no other constructors.
The spec requires a no-arg constructor so that the persistence provider can
create an empty instance. OpenJPA uses it via some tricky generated code
(bytecode insertion).

As for why it's protected instead of public I presume the original devs
thought it was safer to restrict access to the generated constructor. It
isn't documented in the manual, but you could go diving in PCEnhancer.java
(which generates the constructor) and see if there are any comments that
shed some light on the rationale.

-mike

On Fri, Dec 4, 2009 at 2:55 PM, KARR, DAVID (ATTCINW) <dk...@att.com>wrote:

> > -----Original Message-----
> > From: Rick Curtis [mailto:curtisr7@gmail.com]
> > Sent: Friday, December 04, 2009 12:31 PM
> > To: users@openjpa.apache.org
> > Subject: Re: Why does the enhancer create a PROTECTE no-args
> > constructor by default?
> >
> > David-
> >
> > Per the JPA spec --
> >
> > The entity class must have a no-arg constructor. The entity class may
> > have
> > other constructors as well.
> > The no-arg constructor must be public or protected.
> >
> > ...so if your Entity doesn't have one, OpenJPA will do it for you.
>
> Ok, I'll phrase the question again, and perhaps I can make it more
> obvious this time.
>
> Why does the enhancer create a PROTECTED no-args constructor, and not a
> PUBLIC one?
>
> If it was going to create a PUBLIC constructor, there'd be absolutely no
> point to this, because that's exactly what the JVM does.  If the
> enhancer had a good reason to create a PROTECTED constructor instead of
> a PUBLIC one, then I can see why the enhancer would do this, but I still
> see no obvious reason to create a PROTECTED constructor.
>
> Is that clearer now?
>

> > --
> > Thanks,
> > Rick
> >
> > On Fri, Dec 4, 2009 at 1:29 PM, KARR, DAVID (ATTCINW)
> > <dk...@att.com>wrote:
> >
> > > I'm reading the OpenJPA doc, and I see that the enhancer creates a
> > > protected no-args constructor if there is no public one.  Why
> exactly
> > > does it do that?  What is the point of creating a protected
> > constructor
> > > instead of letting the JVM create the public one?  The doc only says
> > > that it does this, not why.
> > >
>

RE: Why does the enhancer create a PROTECTE no-args constructor by default?

["KARR, DAVID (ATTCINW)" <dk...@att.com>]

> -----Original Message-----
> From: Rick Curtis [mailto:curtisr7@gmail.com]
> Sent: Friday, December 04, 2009 12:31 PM
> To: users@openjpa.apache.org
> Subject: Re: Why does the enhancer create a PROTECTE no-args
> constructor by default?
> 
> David-
> 
> Per the JPA spec --
> 
> The entity class must have a no-arg constructor. The entity class may
> have
> other constructors as well.
> The no-arg constructor must be public or protected.
> 
> ...so if your Entity doesn't have one, OpenJPA will do it for you.

Ok, I'll phrase the question again, and perhaps I can make it more
obvious this time.

Why does the enhancer create a PROTECTED no-args constructor, and not a
PUBLIC one?

If it was going to create a PUBLIC constructor, there'd be absolutely no
point to this, because that's exactly what the JVM does.  If the
enhancer had a good reason to create a PROTECTED constructor instead of
a PUBLIC one, then I can see why the enhancer would do this, but I still
see no obvious reason to create a PROTECTED constructor.

Is that clearer now?

> --
> Thanks,
> Rick
> 
> On Fri, Dec 4, 2009 at 1:29 PM, KARR, DAVID (ATTCINW)
> <dk...@att.com>wrote:
> 
> > I'm reading the OpenJPA doc, and I see that the enhancer creates a
> > protected no-args constructor if there is no public one.  Why
exactly
> > does it do that?  What is the point of creating a protected
> constructor
> > instead of letting the JVM create the public one?  The doc only says
> > that it does this, not why.
> >